The present invention is directed to an aluminum alloy composition, an article made from the composition and a method of use and, in particular, to a composition which combines the properties of machinability, brazeability, corrosion resistance and strength.
In the prior art, the use of aluminum alloy compositions in heat exchanger applications is well known. Aluminum alloys are used for heat exchanger headers, tubing, fins and connector blocks. Typically, the connector blocks are brazed to the header to facilitate the hookup of fluid supply and takeaway lines of a system requiring fluid cooling, e.g., an air conditioning system.
When manufacturing the heat exchanger assemblies, the components are often clamped together and furnace brazed using either clad materials, filler brazing materials or a combination of both.
One significant problem that occurs during the manufacturing of the assembly is the formation of an inferior brazing joint between the connector block and the heat exchanger header. Prior to brazing, the connector blocks are often machined and combined with fasteners to facilitate connection to the fluid supply or takeaway lines. Because of the physical property requirements associated with the machining and the fastener use, prior art connector blocks are usually made from AA6000 series aluminum alloys. These types of aluminum alloys exhibit poor machinability and are not easily brazed due to their high magnesium content, especially in a controlled atmosphere brazing process. Consequently, it is often difficult to obtain a high quality brazed joint between the connector block and another component of a heat exchanger assembly. Utilizing a more brazeable alloy such as a standard or commercial AA3000 series alloy does not present an acceptable alternative as a material for connector block use. The AA3000 series alloys, while being brazeable, are generally too soft to adequately machine or have the necessary mechanical properties to facilitate mechanically fastening the connector block to other components.
As such, a need has developed to provide an improved composition for heat exchanger application or other uses where machinability, brazeability, strength and corrosion resistance are required. In response to this need, the present invention provides an improved aluminum alloy composition and an article made therefrom which combines machinability, strength, corrosion resistance and brazeability. The inventive aluminum alloy article has the required mechanical properties making it especially suitable for use as a heat exchanger component. The aluminum alloy composition and article also facilitate brazing processes when assembling the inventive article with other components.
Accordingly, it is a first object of the present invention to provide an aluminum alloy composition exhibiting machinability and brazeability.
Another object of the present invention is to provide an aluminum alloy composition having good corrosion resistance and mechanical properties.
One other object of the present invention is to provide an aluminum alloy article made from the inventive composition.
A still further object of the present invention is to provide a method of brazing the aluminum alloy article.
Other objects and advantages of the present invention will become apparent as a description thereof proceeds.
In satisfaction of the foregoing objects and advantages, the present invention provides an aluminum alloy composition consisting essentially of, in weight percent, up to about 0.6% silicon, up to about 1.2% iron, up to about 0.7% copper, between about 0.1 and 1.8% manganese, up to about 1.5% magnesium, up to about 0.4% chromium, up to about 0.4% zinc, up to about 0.2% zirconium, between about 0.03 and 0.4% titanium, and at least one free machining element selected from the group consisting of bismuth, indium and tin or a compound thereof, wherein each of the bismuth and tin are up to about 1.5% and the indium ranges between about 0.05 and 0.5%, with the balance being aluminum and incidental impurities.
The alloy composition has more preferred limits wherein the silicon is up to about 0.2%, the iron is up to about 0.7%, the copper is up to about 0.5%, the manganese ranges between about 0.2 and 1.7%, the magnesium is up to about 0.8%, the chromium is up to about 0.2%, the zinc is up to about 0.25%, and the titanium ranges between about 0.03 and 0.3%. The ranges of the at least one free machining element are further defined wherein tin and bismuth are each up to about 1.3% and the indium ranges between about 0.05 and 0.3%.
In another embodiment, the silicon ranges between about 0.03 and 0.12%, the iron ranges between about 0.03 and 0.4%, the copper ranges between about 0.01 and 0.5%, the manganese ranges between about 0.5 and 1.6%, the magnesium is up to about 0.7%, the chromium is up to about 0.1%, and the titanium ranges between about 0.03 and 0.2%. The ranges of the at least one free machining element are further defined wherein tin and bismuth are each up to about 1.0% and the indium ranges between about 0.05 and 0.2%. Other embodiments are described below.
In yet another embodiment, the alloy composition has limits wherein the silicon ranges between 0.01 and 0.15%, the iron ranges between 0.01 and 0.5%, the copper, ranges between 0.01 and 0.4%, the manganese ranges between 0.2 and 1.7%, the magnesium is from zero up to 0.4%, an amount of chromium is up to 0.2%, an amount of zinc is up to 0.25%, an amount of zirconium is up to 0.3%, titanium ranges between 0.03 and 0.3%, and an amount of at least one of tin and bismuth is up to 1.3%.
The invention also includes an article made from the inventive alloy composition. A preferred article is one that is machined and brazed. An example of such an article is a heat exchanger component which includes at least one machined portion such as a passageway, recess, seat, threaded portion or the like, e.g., a heat exchanger connector block. The component can include more than one passageway or machined portion and fasteners secured thereto to facilitate connecting the component to other components or structure.
The invention also comprises the article in combination with another component, for example, a connector block and a heat exchanger assembly wherein the assembly has cooling tubes, fins, headers and fluid supply and takeaway lines.
A further aspect of the invention includes an improved brazing process wherein the inventive article is brazed using a flux. The article permits effective brazing with minimal amounts of flux.